two wheeled cart for shopping with an additional wheel pivottante that might rest on three wheels instead of two, in order to make it 'freestanding

• 1. human powered trolley wheels, shopping cart wheel parts and wheel kit assembly and wheel assembly methods [P] . BR112015016687A2 . 2017-07-11

  机译： 人力手推车车轮，购物车车轮零件和车轮套件的组装以及车轮的组装方法

• 2. device for a wheel on the frame - or of a shopping cart and shopping cart whose wheels are so montat [P] . IT989271B . 1975-05-20

  机译： 框架上的轮子的设备-或轮子如此蒙太奇的购物车和购物车的设备

• 3. Pushcart for use in self-service shops, makes wheel diameter of each front caster wheel greater than that of each rear caster wheel [P] . 德国专利： DE202006011849U1 . 2006-12-21

  机译： 用于自助商店的手推车，使每个前脚轮的轮径都大于每个后脚轮的轮径

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• 2. The effects of a selected wheel design and caster fixture design on pushing force when pushing four wheeled industrial carts. [D] . Wein, David S. 2014
• 3. CART-WHEEL.org: An Ethically Approved Online Database for Patient-Entered Data to Facilitate Rare Cancer Research [O] . Damien Kee, Clare Parker, Susie Bae, -1
• 4. A study on bullock carts. Part 1. Engineering analysis of the two-wheel bullock cart design [O] . Raghavan MR, Nagendra HR 1979